Many of the islands of the Aleutians are made up of an unusual geologic formation called columnar basalt. These formations are formed by the cooling of igneous materials. The Aleutians are part of the Pacific "Rim of Fire", made up of numerous volcanoes and geologically active landforms. In this image, biologists with the Alaska Maritime National Wildlife Refuge, explore a sea cave.

Image courtesy of the photographer and the U.S. Fish and Wildlife Digital Library System (http://images.fws.gov/default.cfm?fuseaction=records.display&CFID=646532&CFTOKEN=42735323&id=AA7B5F51%2DC6C4%2D63B9%2D3690491C9F2867C1).Please cite the photographer and the U.S. Fish and Wildlife Digital Library System when using this image.

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